A host of pro-inflammatory and cellular stress induces inflammatory response in chondrocytes, leading to upregulation of matrix metalloproteinases (MMPs) and aggrecanases that degrade the cartilage matrix. Chronic deregulation of these catabolic pathways is suspected of causing osteoarthritis. Regardless of the sources of inflammation, the downstream signals all converge on a common mechanism that activates transcription of all primary response genes. This regulatory point is controlled by the transcription factor cyclin-dependent kinase 9 (CDK9) and its T-type cyclin partner. It was believed for many years that the rate-limiting step in transcriptional activation is the recruitment of transcription factors and RNA Polymerase II (Pol II) to gene promoters. However, recent studies on primary response genes have shown that in their basal and unstimulated states, Pol II is already pre-assembled but is paused at the promoters (Hargreaves, et al., Cell 2009, 138:129-45; Zippo, et al., Cell 2009, 138:1122-36). The rapid activation of these genes is the result of signal-induced recruitment of CDK9 to the promoters, where it phosphorylates Pol II. Phosphorylation by CDK9 induces a conformational change that allows Pol II to enter possessive elongation to efficiently transcribe full-length mRNAs (Zhou and Yik, MMBR 2006, 70(3): 646-659). Given that CDK9 controls a common mechanism of transcriptional activation of inducible genes, it is an effective target for inhibiting the undesirable inflammatory responses from diverse cellular stress, such as sports-related injuries. The present invention is based, in part, on the discovery that pharmacological CDK9 inhibitors, e.g., flavopiridol, and analogs and salts thereof, can effectively suppress primary inflammatory genes in human articular chondrocytes in vitro. Effective suppression of inflammatory responses allows for longer storage life for osteochondral explants used commonly in cartilage repair, and also has therapeutic implications in preventing cartilage breakdown in post-traumatic osteoarthritis.
Severe combat trauma such as those received from explosive devices cause devastating damage to the human body, resulting in dramatic tissue loss, burns, orthopaedic injuries, and hemorrhagic shock. The reaction to such severe polytrauma can include a whole body response called systemic inflammatory response syndrome (SIRS). SIRS is the results of an exaggerated production of pro-inflammatory cytokines that illicit an overwhelming inflammatory response throughout the entire body. While a controlled local inflammation facilitates wound healing, the overwhelming inflammatory response of SIRS significantly increases the risk of life-threatening events such as multiple organ dysfunction and failure. Surgical treatment of injuries is often delayed after polytrauma due to the risk of SIRS-induced organ failure or death. This delays recovery and increases associated medical costs. No pharmacologic agents effectively prevent the onset of SIRS or significantly improve its outcome; there is an urgent need to develop such drugs. Current anti-inflammatory treatments are ineffective in part because they target individual cytokines and pathways, but in SIRS there are simply too many cytokines and pathways involved.
Since the problems of SIRS stem from the activation of the inflammatory response, the conventional approaches to prevent SIRS have targeted one or several of the many individual inflammatory signals or pathways. The results from these studies are mostly disappointing. Severe traumatic injuries activate too many inflammatory signals and pathways, with significant cross talk between the pathways, for this one-by-one approach to be effective. The diverse inflammatory signals propagate through dozens of different cell surface receptors and an intricate network of intracellular signaling pathways, which are then transmitted into the cell nucleus for the activation of thousands of inflammatory mediator genes. To make matters worse, the inflammatory receptors and signaling pathways have multiple levels of redundancy and cross talk. Therefore, no single agent that targets only a specific inflammatory receptor/mediator, signaling pathway, or cell type can prevent SIRS. It is also impractical to formulate a drug cocktail that targets all known inflammatory mediators and pathways at once. In addition, the initial exaggerated pro-inflammatory response in SIRS is activated rapidly after trauma; and therefore, the ideal anti-SIRS agents must also be able to act almost as quickly.